Research from the USA reveals that smog destroys the scent that attracts bees and other pollinators to flowers

Bees must spend more time searching for food while plants have a lower chance of being pollinated, reveals air pollution research.

Honeybees at Kew

Ozone smog destroys the scent that attracts bees and other pollinators to flowers, say American researchers. Their findings have big implications both for plants and insects, and could help to explain the worldwide decline in pollinators.

The scent of flowers contains volatile organic compounds that travel long distances in the air. Once an insect picks up the scent of its favourite food plant, it can follow the trail back to its source.

But ozone smog – a mixture of ozone and other highly reactive chemicals – can neutralise the fragrance before it gets very far. The result is that many insects must spend more time searching for food, while plants have a lower chance of being pollinated.

Higher ozone levels

Two hundred years ago, the air contained a very low concentration of ozone, around 20 parts per billion. Today, the output from vehicle exhausts and industrial pollution can send the concentration soaring six times as high.

Quinn McFrederick, Jose Fuentes and James Kathilankal at the University of Virginia compared how well three volatile molecules, each a common component of floral scent, would have fared in the clean air of pre-industrial America with what happens to them in today’s polluted air.

In pre-industrial air, they found that 80 per cent of the scent molecules survived 1km downwind of a flower. In smoggy air they found this sort of concentration only within 200m of a flower.

Pollution is unlikely to affect honeybees, says McFrederick, because beekeepers site their hives near crops. “But there are bees that are specialists, such as the squash bee that needs to find pumpkin or squash flowers to raise young. For these bees, the destruction of scent trails by pollution could be very important.”

Bee research

Two years ago a major international study led by Koos Biesmeijer at the University of Leeds found a major decline in the diversity of bee species in Britain, the Netherlands and Europe.

At the moment it’s impossible to say how much air pollution is contributing to the decline, says Biesmeijer. “But since this research was published I have been talking to colleagues about how we might study the effect of air pollution.”